The present invention relates to the sterilization and disinfection arts. It finds particular application in conjunction with electrochemically produced solutions containing oxidizing agents, such as peracetic acid, hydrogen peroxide, and ozone, for sterilization or disinfection of medical and pharmaceutical equipment, and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable to other sterilization, disinfection, and sanitization methods employing such oxidizing agents, including treatment of water, food, food service equipment, and the like.
Oxidizing agents, such as peracetic acid, hydrogen peroxide, and ozone, are useful disinfectants and sterilants for a variety of applications. Peracetic acid has a number of uses, including disinfection of waste and sterilization of medical equipment, packaging containers, food processing equipment, and the like. Peracetic acid poses few disposal problems because it decomposes to compounds which are readily degraded in sewage treatment plants. It has a broad spectrum of activity against microorganisms, and is effective even at low temperatures. Hydrogen peroxide is used for sterilization of medical equipment. Ozone has been used extensively for disinfection and treatment of water and, more recently, for treatment of food and food service equipment.
Conventionally, to form peracetic acid, peracetic acid precursors are mixed with water and other chemicals in a bath. Items to be decontaminated, either by sterilization or disinfection, are then immersed in the bath for a sufficient period to effect the required level of decontamination. The decontaminated items are then typically rinsed before use. To ensure effective sterilization or disinfection within a preselected period of time, the concentration of peracetic acid is maintained above a minimum effective level, typically around 2300 ppm for sterilization of medical instruments. When the peracetic acid concentration is at or above the minimum effective level for sterilization, complete sterilization is expected. Lower levels of peracetic acid are effective as disinfectants. Concentrations as low as 2-10 ppm, or less, have been shown to be effective for disinfection, which requires only the destruction of pathogenic microorganisms.
In facilities where items are being sterilized or disinfected at frequent intervals throughout the day, the same batch of peracetic acid solution is often used repeatedly. However, peracetic acid tends to decompose over time. For example, a bath which is above the minimum effective peracetic acid concentration for sterilization of around 2300 ppm at the beginning of a day, frequently drops to around 800 ppm, well below the effective concentration, without further additions of the peracetic acid precursors. Elevated ambient temperatures, the quantity of items sterilized or disinfected, and the degree of contamination of the items, all contribute to reducing the useful life of the bath. In addition, storage conditions sometimes lead to degradation of the peracetic acid precursors before use.
Moreover, the precursors are often hazardous materials which sometimes pose shipment and storage problems. Because of the risks of storage and also the fact that they degrade over time, it is preferable to maintain a limited supply of the precursors and reorder them at frequent intervals.
For hydrogen peroxide and ozone, similar problems arise. Ozone is a particularly short lived species which decomposes readily. Hydrogen peroxide tends to decompose to water and oxygen.
Recently, the cleaning and decontamination properties of solutions formed by the electrolysis of water under special conditions have been explored. Electrolysis devices are known which receive a supply of water, such as tap water, commonly doped with a salt, and perform electrolysis on the water. During electrolysis, an anolyte solution is produced from the doped water at an anode and a catholyte solution is produced at a cathode. Examples of such water electrolysis units are as described in U.S. Pat. Nos. 5,635,040; 5,628,888; 5,427,667; 5,334,383; 5,507,932; 5,560,816; and 5,622,848 , whose disclosures are incorporated herein by reference.
To create these anolyte and catholyte solutions, tap water, often with an added electrically or ionically conducting agent such as halogen salts including the salts sodium chloride and potassium chloride, is passed through an electrolysis unit or module which has at least one anodic chamber and at least one cathodic chamber, generally separated from each other by a partially-permeable barrier. An anode contacts the water flowing in the anodic chamber, while a cathode contacts the water flowing in the cathodic chamber. The anode and cathode are connected to a source of electrical potential to expose the water to an electrical field. The barrier may allow the transfer of selected electron carrying species between the anode and the cathode but limits fluid movement between the anodic and cathodic chambers. The salt and minerals naturally present in and/or added to the water undergo oxidation in the anodic chamber and reduction in the cathodic chamber.
An anolyte resulting at the anode and a catholyte resulting at the cathode can be withdrawn from the electrolysis unit. The anolyte and catholyte may be used individually or as a combination. The anolyte has been found to have anti-microbial properties, including anti-viral properties. The catholyte has been found to have cleaning properties.
However, electrochemically activated water is not without shortcomings. Electrochemically activated water has a high surface energy which does not readily allow for penetration of the electrochemically activated water into creviced areas of medical instruments. Thus, complete kill may not be achieved. Further problems have arisen on metal surfaces coming into contact with the electrochemically activated water, including the surfaces of the decontamination equipment and metal medical devices. The electrochemically activated water is corrosive to certain metals. Stainless steel, used to produce many medical devices, is particularly susceptible to corrosion by electrochemically activated water.
Other chemicals are also amenable to electrochemical conversion. Khomutov, et al. ("Study of the Kinetics of Anodic Processes in Potassium Acetate," Izv. Vvssh. Uchebn. Zaved., Khim. Teknol . 31 (11) pp. 71-74 (1988)) discloses a study of the conversion of acetate solutions to peracetic acid and acetyl peroxide in the temperature range of -10.degree. C. to 20.degree. C. using a three-electrode cell. The anode and cathode regions of the cell were separated by a barrier of porous glass. Anodes of platinum, gold or carbon, at a potential of 2-3.2 V relative to a silver/silver chloride reference electrode, were used in the study. Potassium acetate concentrations were initially 2-10 mol/L. From conductivity and viscosity measurements, Khomutov, et al. estimated that peracetic acid solutions were generated at the anode with concentrations of active oxygen of 0.1 gram equivalents/L. However, no direct measurements of peracetic acid concentration in the bulk solution were made. Moreover, the pH range of 8.2-10.4 disclosed by Khomutov, et al. is undesirable for many practical decontamination solutions. To reduce corrosion of the metal components of the instruments to be decontaminated, a pH of close to neutral is desirable.
The present invention provides a new and improved system for generation of peracetic acid and other oxidizing agents which overcomes the above referenced problems and others.